fix: correct task scheduling and simplify agent internals

Fix queue cancellation, concurrency limits and worker status updates.

Use direct Explorer imports, split the Diagnoser loop into helpers and remove unused tool registration and prompt-builder code.

Correct model caching, endpoint selection and retry handling.

artemis/runtime/adb_endpoint.py

@@ -166,3 +166,8 @@ def current_adb_endpoint() -> AdbEndpoint:
     host = settings.ADB_HOST or os.environ.get("ADB_HOST") or DEFAULT_ADB_HOST
     port = settings.ADB_PORT or os.environ.get("ADB_PORT") or DEFAULT_ADB_PORT
     return AdbEndpoint.create(str(host), int(port))
+
+
+def adb_command(arguments: Sequence[str]) -> list[str]:
+    """Resolve the ADB binary and add the configured server's host and port."""
+    return AdbSession(current_adb_endpoint()).command(arguments)